Hepatic fatty acid transporter Cd36 is a common target of LXR, PXR, and PPARgamma in promoting steatosis

Role of oxysterol 4β-hydroxycholesterol and liver X receptor alleles in pre-eclampsia

BACKGROUND

Liver X receptors (LXRs) are expressed in placenta and may be associated with pre-eclampsia (PE). Oxysterols act as agonists for LXRs. We recently proposed a new blood pressure-regulating circuit with oxysterol 4β-hydroxycholesterol (4βHC) acting as a hypotensive factor via LXRs.

MATERIALS AND METHODS

This study investigated the association between maternal plasma 4βHC, blood pressure (BP) indices, placental expression of LXR target genes, and patient characteristics using data from the Finnish Genetics of Pre-Eclampsia Consortium (FINNPEC) cohort. Plasma samples of 144 women with PE and 38 healthy pregnant controls as well as 44 PE and 40 control placental samples were available. In addition, genetic data from the FinnGen project was utilized to explore the associations of LXR alleles with PE and pregnancy hypertension.

RESULTS

There were no significant associations between 4βHC and BP or maternal and perinatal characteristics in FINNPEC cohort. However, plasma 4βHC was inversely correlated with the maternal body mass index. There were no associations with the genetic variants of LXRs with PE in FinnGen. LXR target genes APOD, SCARB1, TGM2, and LPCAT3 were expressed differently between PE and normal pregnancies in placental samples of FINNPEC.

CONCLUSIONS

Our results demonstrate that plasma 4βHC and genetic LXR variants do not play a major role in PE and BP regulation during pregnancy. However, key LXR target genes involved in lipid metabolism were expressed differently in normal and PE pregnancies. Further research is needed to understand the complexities of oxysterols, LXRs, and their potential contributions to placental function and pregnancy outcomes.

Farnesoid X receptor‑driven metabolic plasticity: Bridging physiological adaptation and malignant transformation in lipid handling (Review)

Metabolic reprogramming represents a hallmark of malignant tumors, manifested through progressive alterations in nutrient utilization patterns during oncogenesis. As fundamental constituents of biological membranes, essential components of signaling pathways, and critical energy substrates, lipids undergo comprehensive metabolic restructuring in neoplastic cells. This lipid remodeling confers enhanced adaptability to sustain uncontrolled proliferation while promoting aggressive migratory phenotypes. Farnesoid X receptor (FXR), a ligand‑activated nuclear receptor responsive to bile acid (BA) derivatives and cholesterol metabolites, orchestrates key aspects of lipid homeostasis. Its regulatory network encompasses cholesterol/BA metabolism, fatty acid (FA) metabolism and plasma lipoprotein trafficking pathways. Emerging evidence positions FXR as a pleiotropic modulator in oncogenesis, with dysregulated expression patterns documented across multiple tumor lineages and premalignant lesions. This mechanistic understanding has propelled FXR‑targeted therapeutics into the forefront of precision oncology development. The present review critically examines the FXR‑lipid axis in lipid‑enriched malignancies, with particular emphasis on its regulatory circuitry governing BA flux and FA turnover.

Transcription factors, metabolic dysfunction-associated fatty liver disease, and therapeutic implications

Metabolic dysfunction-associated fatty liver disease (MAFLD) encompasses a spectrum of liver diseases ranging from metabolic dysfunction-associated fatty liver to metabolic dysfunction-associated steatohepatitis, which may progress to liver cirrhosis and hepatocellular carcinoma. Several mechanisms, including obesity, insulin resistance, dyslipidemia, inflammation, apoptosis, mitochondrial dysfunction, and reactive oxygen species, have been proposed to underlie the progression of MAFLD. Transcription factors are proteins that specifically bind to DNA sequences to regulate the transcription of target genes. Numerous transcription factors regulate MAFLD by modulating the transcription of genes involved in steatosis, inflammation, apoptosis, and fibrosis. Here, we review the pathological factors associated with MAFLD, with a particular emphasis on the transcription factors that contribute to the progression of MAFLD and their therapeutic implications.

Neurotensin promotes hepatic steatosis by regulating lipid uptake and mitochondrial adaptation in hepatocytes

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a multifactorial disease characterized by hepatic steatosis. Mitochondrial dysfunction resulting in the incomplete digestion of surplus fat is one of the key factors that lead to hepatic steatosis but the reason for this remains unclear. We investigated the role of neurotensin (NTS), a gut hormone, in inducing maladaptive fat metabolism in steatotic liver. We identify CD36 and PGC1α, two critical drivers of MASLD, as direct NTS signaling targets in the liver. NTS upregulates CD36, a free fatty acid receptor, in hepatocytes and promotes long chain lipid uptake. Conversely, NTS inhibits PGC1α, which acts as a lipid sensor and translocates to the nucleus to activate lipid catabolism-related genes in an AMPK-dependent manner. Thus, a high fat diet decreases the fatty acid oxidation and oxidative phosphorylation capacity of the liver and hepatocytes from NTS or NTS receptor 1 (NTSR1) wild type mice; whereas NTS deficiency preserves the lipid metabolism capacity of the liver. NTS signaling is significantly upregulated in MASLD and in metabolic dysfunction-associated steatohepatitis (MASH) human liver samples when compared to normal livers, which correlates with the expression of CD36 and oxidative phosphorylation proteins. These findings provide critical mechanistic insights into the maladaptive fat metabolism noted with steatosis in mice and humans and suggest novel strategies for therapeutic intervention of MASLD, which affects nearly one-quarter of the global population.

Evaluation of FXR Activity in Pollutants Identified in Sewage Sludge and Subsequent in Vitro and in Vivo Characterization of Metabolic Effects of Triphenyl Phosphate

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common liver disease worldwide, and increasing evidence suggests that exposure to environmental pollutants is associated with the increased incidence of MASLD. The farnesoid X receptor (FXR) plays an important role in the development of MASLD by regulating bile acids (BAs) and lipid metabolism. However, whether FXR-active pollutants are the environmental drivers of MASLD remains unclear.

OBJECTIVES

This study aimed to determine whether FXR-active pollutants exist in the environment and evaluate their ability to trigger MASLD development in mice.

METHODS

An FXR protein affinity pull-down assay and nontargeted mass spectrometry (MS) analysis were used to identify environmental FXR ligands in sewage sludge. A homogeneous time-resolved fluorescence coactivator recruitment assay and cell-based dual-luciferase reporter assay were used to determine the FXR activities of the identified pollutants. Targeted analysis of BAs, MS imaging, lipidomic analysis, 16S rRNA sequencing, and quantitative polymerase chain reaction were conducted to assess the ability of FXR-active pollutants to induce metabolic disorders of BAs and lipids and to contribute to MASLD development in C57BL/6N mice.

RESULTS

We identified 19 compounds in the sewage sludge that had FXR-antagonistic activity, and triphenyl phosphate (TPHP) was the FXR antagonist with the highest efficacy. Mice exposed to either 10 or 50 mg / kg TPHP for 30 d had higher levels of conjugated primary BAs in enterohepatic circulation, and the BA pool showed FXR antagonistic activities. The exposed mice also had greater lipogenesis (more Oil Red O staining and high triglyceride levels) in liver.

CONCLUSIONS

Nineteen FXR-antagonistic pollutants were identified in sewage sludge. FXR inhibition by the strongest antagonist TPHP may have a role in promoting MASLD development in mice by inducing a positive feedback loop between the FXR and BAs. https://doi.org/10.1289/EHP15435.

Liver specific transgenic expression of CYP7B1 attenuates early western diet-induced MASLD progression

Effect of liver specific oxysterol 7α-hydroxylase (CYP7B1) overexpression on the Western diet (WD)-induced metabolic dysfunction-associated steatotic liver disease (MASLD) progression was studied in mice. Among various hepatic genes impacted during MASLD development, CYP7B1 is consistently suppressed in multiple MASLD mouse models and in human MASLD cohorts. CYP7B1 enzyme suppression leads to accumulations of bioactive oxysterols such as (25R)26-hydroxycholesterol (26HC) and 25-hydroxycholesterol (25HC). We challenged liver specific CYP7B1 transgenic (CYP7B1hep.tg) overexpressing mice with ad libitum WD feeding. Unlike their WT counterparts, WD-fed CYP7B1hep.tg mice developed no significant hepatotoxicity as evidenced by liver histology, lipid quantifications, and serum biomarker analyses. Hepatic 26HC and 25HC levels were maintained at the basal levels. The comparative gene expression/lipidomic analyses between WT and CYP7B1hep.tg mice revealed that chronically accumulated 26HC initiates LXR/PPAR-mediated hepatic fatty acid uptake and lipogenesis which surpasses fatty acid metabolism and export; compromising metabolic functions. In addition, major pathways related to oxidative stress, inflammation, and immune system including retinol metabolism, arachidonic acid metabolism, and linoleic acid metabolism were significantly impacted in the WD-fed WT mice. All pathways were unaltered in CYP7B1hep.tg mice liver. Furthermore, the nucleus of WT mouse liver but not of CYP7B1hep.tg mouse liver accumulated 26HC and 25HC in response to WD. These data strongly suggested that these two oxysterols are specifically important in nuclear transcriptional regulation for the described cytotoxic pathways. In conclusion, this study represents a "proof-of-concept" that maintaining normal mitochondrial cholesterol metabolism with hepatic CYP7B1 expression prevents oxysterol-driven liver toxicity; thus attenuating MASLD progression.

The fungicide propiconazole induces hepatic steatosis and activates PXR in a mouse model of diet-induced obesity

Propiconazole is a triazole fungicide previously shown to induce triglyceride accumulation in human liver HepaRG cells, potentially via activation of the Pregnane X Receptor (PXR). However, whether propiconazole can disrupt hepatic and whole-body metabolism in vivo is currently unknown. Therefore, we aimed to examine the metabolic effects of propiconazole in the context of metabolic dysfunction-associated steatotic liver disease (MASLD), obesity, and insulin resistance. To this end, male C57BL/6J mice were fed a high-fat diet for 20 weeks. During the last 10 weeks, mice additionally received vehicle, 0.04, 30, or 100 mg/kg body weight (bw)/day propiconazole via oral gavage. High-dose propiconazole, but not low or intermediate dose, reduced body weight gain and adipose tissue weight in obese mice. Mice receiving high-dose propiconazole displayed improved glucose tolerance and reduced levels of plasma triglycerides and cholesterol. Propiconazole dose-dependently increased liver weight and triglyceride levels and at high dose caused signs of hepatic inflammation. RNA sequencing on the liver revealed that propiconazole mainly induced PXR target genes. At intermediate and high dose, propiconazole induced pathways related to cell-cell interactions and inflammation, while oxidative phosphorylation was repressed by propiconazole. Comparison of gene regulation in wildtype and PXR knockout primary hepatocytes as well as gene reporter assays confirmed the activation of PXR by propiconazole. All in all, our data underscore the capacity of propiconazole to activate PXR in the liver and thereby promote the development of hepatic steatosis in vivo.

Protocatechuic Acid Suppresses Lipid Uptake and Synthesis through the PPARγ Pathway in High-Fat Diet-Induced NAFLD Mice

Nonalcoholic fatty liver disease (NAFLD) has become one of the most concerning health problems in the world. Dietary intervention is an effective way to prevent and improve NAFLD. As one of the main metabolites of anthocyanins, protocatechuic acid (PCA) exhibited strong activity to improve NAFLD, but the specific mechanism remains unclear. Currently, proteomics has been used to identify that PCA treatment could significantly influence the expression of 224 proteins, including 89 downregulated proteins and 135 upregulated proteins. KEGG analysis showed that PCA obviously inhibited the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Immunofluorescence and Western blot analyses further confirmed that PCA repressed the protein expression of PPARγ and subsequently inhibited the expression of free fatty acid (FFA) uptake proteins (CD36 and FABP2) and FFA synthesis proteins (ACC and FASN), respectively. These effects of PCA contributed to the inhibitory activity of excessive lipid accumulation in the liver. Our results highlighted that PCA could effectively alleviate high-fat diet-induced (HFD) NAFLD by inhibiting lipid absorption and synthesis through the PPARγ signaling pathway.

The hypolipidemic effect of MI-883, the combined CAR agonist/ PXR antagonist, in diet-induced hypercholesterolemia model

Constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are closely related nuclear receptors with overlapping regulatory functions in xenobiotic clearance but distinct roles in endobiotic metabolism. Car activation has been demonstrated to ameliorate hypercholesterolemia by regulating cholesterol metabolism and bile acid elimination, whereas PXR activation is associated with hypercholesterolemia and liver steatosis. Here we show a human CAR agonist/PXR antagonist, MI-883, which effectively regulates genes related to xenobiotic metabolism and cholesterol/bile acid homeostasis by leveraging CAR and PXR interactions in gene regulation. Through comprehensive analyses utilizing lipidomics, bile acid metabolomics, and transcriptomics in humanized PXR-CAR-CYP3A4/3A7 mice fed high-fat and high-cholesterol diets, we demonstrate that MI-883 significantly reduces plasma cholesterol levels and enhances fecal bile acid excretion. This work paves the way for the development of ligands targeting multiple xenobiotic nuclear receptors. Such ligands hold the potential for precise modulation of liver metabolism, offering new therapeutic strategies for metabolic disorders.

Deciphering the Role of CD36 in Gestational Diabetes Mellitus: Linking Fatty Acid Metabolism and Inflammation in Disease Pathogenesis

Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications which exerts detrimental effects on mothers and children. Emerging evidence has pointed to the important role of the fatty acid transporter protein CD36 in the pathogenesis of GDM. As a heavily glycosylated transmembrane protein, CD36 is widely expressed in diverse cell types, including placental trophoblasts, monocytes/macrophages, adipocytes, and pancreatic cells et al. CD36 plays a key role in lipid metabolism and signal transduction in the pathophysiological mechanism of GDM. The modified expression and functionality of CD36 may contribute to inflammation and oxidative stress in maternal tissues, interfere with insulin signaling, and subsequently influence maternal insulin sensitivity and fetal growth, increasing the risk for GDM. This review provides an overview of the current knowledge regarding the expression and function of CD36 in various tissues throughout pregnancy and explores how CD36 dysregulation can activate inflammatory pathways, worsen insulin resistance, and disrupt lipid metabolism, thereby complicating the necessary metabolic adjustments during pregnancy. Furthermore, the review delves into emerging therapeutic approaches targeting CD36 signaling to alleviate the impacts of GDM. Understanding the involvement of CD36 in GDM could yield crucial insights into its mechanisms and potential interventions for enhancing maternal and fetal health outcomes.

TMEM135 deficiency improves hepatic steatosis by suppressing CD36 in a SIRT1-dependent manner

OBJECTIVES

Dysregulation of lipid homeostasis pathway causes many liver diseases, including hepatic steatosis. One of the primary factors contributing to lipid accumulation is fatty acid uptake by the liver. Transmembrane protein 135 (TMEM135), which exists in mitochondria and peroxisomes, participates in intracellular lipid metabolism. This study aims to investigate the role of TMEM135 on regulating cellular lipid import in the liver.

METHODS

We used in vivo, ex vivo, and in vitro models of steatosis. TMEM135 knockout (TMEM135KO) and wild type (WT) mice were fed a high-fat diet (HFD) to induce hepatic steatosis. Primary mouse hepatocytes and AML12 cells were treated with free fatty acid (FFA). Additionally, TMEM135-deficient stable cells and overexpressed cells were established using AML12 cells.

RESULTS

TMEM135 deficiency mitigated lipid accumulation in the liver of HFD-fed TMEM135KO mice. TMEM135-depleted primary hepatocytes and AML12 cells exhibited less lipid accumulation when treated with FFA compared to control cells, as shown as lipid droplets. Consistently, the effect of TMEM135 depletion on lipid accumulation was completely reversed under TMEM135 overexpression conditions. CD36 expression was markedly induced by HFD or FFA, which was reduced by TMEM135 depletion. Among the SIRT family proteins, only SIRT1 expression definitely increased in the liver of HFD-fed TMEM135KO mice along with a significant increase in NAD+/NADH ratio. However, inhibition of SIRT1 in TMEM135-depleted cells using siSIRT1 or the SIRT1 inhibitor EX-527 resulted in an increase of CD36 expression and consequent TG levels.

CONCLUSIONS

TMEM135 depletion attenuates CD36 expression in a SIRT1-dependent manner, thereby reducing cellular lipid uptake and hepatic steatosis.

Insights of direct and indirect regulation of PXR through phosphorylation in fatty liver disease

The pregnane X receptor (PXR), a ligand-activated nuclear receptor, regulates the transcription of several genes that encode many enzymes and transporters related to drug metabolism. PXR also performs an important role as a physiological sensor in the modulation of endobiotic metabolism for hormones, bile acids, cholesterol, fatty acids, and glucose. Dysregulation of these PXR-mediated pathways is implicated in the progression of metabolic dysfunction-associated steatohepatitis (MASH), contributing to the complex interplay of factors involved in chronic liver disease development and exacerbation affecting millions worldwide. This review highlights the current knowledge of PXR expression and its role in endobiotic metabolism related to MASH development, which is associated with diverse causes and dire outcomes. This review focuses on elucidating the molecular pathways associated with PXR activation directly or indirectly and PXR interaction with other regulatory factors. Although there is still much to comprehend about the intricate details of these pathways, the conclusion is drawn that PXR exerts a crucial role in the pathological and physiological pathways of hepatic cellular processes, which holds promise as a potential pharmacological target for exploring novel therapeutic approaches for MASH treatment and/or prevention. SIGNIFICANCE STATEMENT: The pregnane X receptor (PXR) plays a fundamental role in regulating gene expression involved in xenobiotic and endobiotic metabolism. Dysregulation of PXR-mediated pathways is related to the development of metabolic dysfunction-associated steatohepatitis. The ligand-independent pathways regulating PXR hepatic functions through phosphorylation shed light on possible indirect molecular mechanisms and pathways that regulate PXR activity and function. Understanding these pathways may provide insight into new pharmaceutical interventions for metabolic dysfunction-associated steatohepatitis development.

Hepatocyte-specific SLC27A4 deletion ameliorates nonalcoholic fatty liver disease in mice via suppression of phosphatidylcholine-mediated PXR activation

BACKGROUND

The protein Solute carrier family 27 member 4 (SLC27A4) is crucial for fatty acid synthesis and β-oxidation, but its role in hepatic steatosis and nonalcoholic fatty liver disease (NAFLD) progression is not fully understood.

METHODS

Mice with AAV-mediated overexpression of Slc27a4 in liver and hepatocytes-specific deletion of Slc27a4 were fed a standard chow diet, a high-fat diet (HFD), or a methionine and choline-deficient diet (MCD). Serum and liver tissues were collected and analyzed by biochemical assay, histology, lipidomic analysis, RNA-seq analysis, qPCR, western blot and immunofluorescence.

RESULTS

This study found elevated expression of SLC27A4 in individuals with NAFLD and OAPA-treated MPHs cells, leading to increased lipid accumulation and diet-induced liver steatosis, inflammation, and fibrosis. Conversely, hepatocyte-specific deletion of Slc27a4 improved the development of both NAFLD and NASH. SLC27A4 overexpression resulted in increased hepatic pregnane X receptor (PXR) expression and accumulation of phosphatidylcholine (PC), which activates PXR signaling and inducing SLC27A4 expression. PXR overexpression hinders the protective impact of Slc27a4 deletion on lipid accumulation and inflammation, whereas its deficiency in mice reduces the effect of Slc27a4 overexpression on NAFLD development.

CONCLUSION

These results indicate that SLC27A4 plays a critical role of lipid accumulation and inflammation, and is implicated in the development of NAFLD progression, rendering it potentially actionable target for NAFLD treatment.

CD36: a promising therapeutic target in hematologic tumors

Cluster of differentiation 36 (CD36) is a multiligand receptor with important roles in lipid metabolism, angiogenesis and innate immunity, and its diverse effects may depend on the binding of specific ligands in different contexts. CD36 is expressed not only on immune cells in the tumor microenvironment (TME) but also on some hematopoietic cells. CD36 is associated with the growth, metastasis and drug resistance in some hematologic tumors, such as leukemia, lymphoma and myelodysplastic syndrome. Currently, some targeted therapeutic agents against CD36 have been developed, such as anti-CD36 antibodies, CD36 antagonists (small molecules) and CD36 expression inhibitors. This paper not only innovatively addresses the role of CD36 in some hematopoietic cells, such as erythrocytes, hematopoietic stem cells and platelets, but also pays special attention to the role of CD36 in the development of hematologic tumors, and suggests that CD36 may be a potential cancer therapeutic target in hematologic tumors.

Bach2 repression of CD36 regulates lipid-metabolism-linked effector functions in follicular B cells

The transcription repressor Bach2 plays a crucial role in shaping humoral immunity, but its cell-autonomous function remains elusive. Here, we reveal the mechanism by which Bach2 regulates effector cell maturation in peripheral B cells. In response to Toll-like receptor (TLR) agonists, Bach2 deficiency promotes the differentiation of follicular, but not marginal zone, B cells into effector cells, producing interleukin (IL)-6 and antibodies. This phenomenon is associated with changes in lipid metabolism, such as increases in CD36 expression, lipid influx, and fatty acid oxidation. Consistent with this, Bach2-deficient B cells exhibit elevated levels of mitochondrial oxidative stress, lipid peroxidation, and p38 activation. Mechanistically, Bach2 acts as a repressor of Cd36, and inhibition of CD36 or fatty acid oxidation reduces the differentiation of naive B cells into IL-6- and antibody-secreting cells. These results indicate Bach2 as a key metabolic checkpoint regulator crucial for maintaining a functionally quiescent state of follicular B cells.

Propionate Decreases Microglial Activation but Impairs Phagocytic Capacity in Response to Aggregated Fibrillar Amyloid Beta Protein

Microglia, the innate immune cell of the brain, are a principal player in Alzheimer's disease (AD) pathogenesis. Their surveillance of the brain leads to interaction with the protein aggregates that drive AD pathogenesis, most notably Amyloid Beta (Aβ). Microglia attempt to clear and degrade Aβ using phagocytic machinery, spurring damaging neuroinflammation in the process. Thus, modulation of the microglial response to Aβ is crucial in mitigating AD pathophysiology. SCFAs, microbial byproducts of dietary fiber fermentation, are blood-brain barrier permeable molecules that have recently been shown to modulate microglial function. It is unclear whether propionate, one representative SCFA, has beneficial or detrimental effects on microglia in AD. Thus, we investigated its impact on microglial Aβ response in vitro. Using a multiomics approach, we characterized the transcriptomic, metabolomic, and lipidomic responses of immortalized murine microglia following 1 h of Aβ stimulation, as well as characterizing Aβ phagocytosis and secretion of reactive nitrogen species. Propionate blunted the early inflammatory response driven by Aβ, downregulating the expression of many Aβ-stimulated immune genes, including those regulating inflammation, the immune complement system, and chemotaxis. Further, it reduced the expression of Apoe and inflammation-promoting Aβ-binding scavenger receptors such as Cd36 and Msr1 in favor of inflammation-dampening Lpl, although this led to impaired phagocytosis. Finally, propionate shifted microglial metabolism, altering phospholipid composition and diverting arginine metabolism, resulting in decreased nitric oxide production. Altogether, our data demonstrate a modulatory role of propionate on microglia that may dampen immune activation in response to Aβ, although at the expense of phagocytic capacity.

Activation of pregnane X receptor sensitizes alcoholic steatohepatitis by transactivating fatty acid binding protein 4

Alcoholic steatohepatitis (ASH) is a liver disease characterized by steatosis, inflammation, and necrosis of the liver tissue as a result of excessive alcohol consumption. Pregnane X receptor (PXR) is a xenobiotic nuclear receptor best known for its function in the transcriptional regulation of drug metabolism and disposition. Clinical reports suggested that the antibiotic rifampicin, a potent human PXR activator, is a contraindication in alcoholics, but the mechanism was unclear. In this study, we showed that the hepatic expression of fatty acid binding protein 4 (FABP4) was uniquely elevated in ASH patients and a mouse model of ASH. Pharmacological inhibiting FABP4 attenuated ASH in mice. Furthermore, treatment of mice with the mouse PXR agonist pregnenolon-16α-carbonitrile (PCN) induced the hepatic and circulating levels of FABP4 and exacerbated ASH in a PXR-dependent manner. Our mechanism study established FABP4 as a transcriptional target of PXR. Treatment with andrographolide, a natural compound and dual inhibitor of PXR and FABP4, alleviated mice from ASH. In summary, our results showed that the PXR-FABP4 gene regulatory axis plays an important role in the progression of ASH, which may have accounted for the contraindication of rifampicin in patients of alcoholic liver disease. Pharmacological inhibition of PXR and/or FABP4 may have its promise in the clinical management of ASH.

Elevated systemic total bile acids escalate susceptibility to alcohol-associated liver disease

Excessive alcohol consumption is a major global health problem. Individuals with alcoholic liver disease often exhibit elevated serum total bile acids (TBAs). Nevertheless, the extent to which high TBA contributes to alcohol-associated liver disease (AALD) remains elusive. To investigate this, wild-type mice were categorized into normal (nTBA) and high (hTBA) TBA groups. Both groups underwent chronic-binge ethanol feeding for 4 weeks, followed by additional weekly ethanol doses. Ethanol feeding worsened AALD in both male and female mice with elevated serum TBA, characterized by liver dysfunction and steatosis. Decreased hepatic expression of genes involved in mitochondrial β-oxidation and lipid transport in ethanol-fed hTBA mice suggests that altered fatty acid metabolism contributed to AALD. Our findings, which represent the first to link high serum TBA to increased AALD susceptibility, underscore the importance of proactive serum TBA screening as a valuable tool for identifying individuals at high risk of developing AALD.

Non-mitogenic FGF19 mRNA-based therapy for the treatment of experimental metabolic dysfunction-associated steatotic liver disease (MASLD)

Metabolic dysfunction-associated steatohepatitis (MASH) represents a global health threat. MASH pathophysiology involves hepatic lipid accumulation and progression to severe conditions like cirrhosis and, eventually, hepatocellular carcinoma. Fibroblast growth factor (FGF)-19 has emerged as a key regulator of metabolism, offering potential therapeutic avenues for MASH and associated disorders. We evaluated the therapeutic potential of non-mitogenic (NM)-FGF19 mRNA formulated in liver-targeted lipid nanoparticles (NM-FGF19-mRNAs-LNPs) in C57BL/6NTac male mice with diet-induced obesity and MASH (DIO-MASH: 40% kcal fat, 20% kcal fructose, 2% cholesterol). After feeding this diet for 21 weeks, NM-FGF19-mRNAs-LNPs or control (C-mRNA-LNPs) were administered (0.5 mg/kg, i.v.) weekly for another six weeks, in which diet feeding continued. NM-FGF19-mRNAs-LNPs treatment in DIO-MASH mice resulted in reduced body weight, adipose tissue depots, and serum transaminases, along with improved insulin sensitivity. Histological analyses confirmed the reversal of MASH features, including steatosis reduction without worsening fibrosis. NM-FGF19-mRNAs-LNPs reduced total hepatic bile acids (BAs) and changed liver BA composition, markedly influencing cholesterol homeostasis and metabolic pathways as observed in transcriptomic analyses. Extrahepatic effects included the down-regulation of metabolic dysfunction-associated genes in adipose tissue. This study highlights the potential of NM-FGF19-mRNA-LNPs therapy for MASH, addressing both hepatic and systemic metabolic dysregulation. NM-FGF19-mRNA demonstrates efficacy in reducing liver steatosis, improving metabolic parameters, and modulating BA levels and composition. Given the central role played by BA in dietary fat absorption, this effect of NM-FGF19-mRNA may be mechanistically relevant. Our study underscores the high translational potential of mRNA-based therapies in addressing the multifaceted landscape of MASH and associated metabolic perturbations.

Macrophage-mediated myelin recycling fuels brain cancer malignancy

Tumors growing in metabolically challenged environments, such as glioblastoma in the brain, are particularly reliant on crosstalk with their tumor microenvironment (TME) to satisfy their high energetic needs. To study the intricacies of this metabolic interplay, we interrogated the heterogeneity of the glioblastoma TME using single-cell and multi-omics analyses and identified metabolically rewired tumor-associated macrophage (TAM) subpopulations with pro-tumorigenic properties. These TAM subsets, termed lipid-laden macrophages (LLMs) to reflect their cholesterol accumulation, are epigenetically rewired, display immunosuppressive features, and are enriched in the aggressive mesenchymal glioblastoma subtype. Engulfment of cholesterol-rich myelin debris endows subsets of TAMs to acquire an LLM phenotype. Subsequently, LLMs directly transfer myelin-derived lipids to cancer cells in an LXR/Abca1-dependent manner, thereby fueling the heightened metabolic demands of mesenchymal glioblastoma. Our work provides an in-depth understanding of the immune-metabolic interplay during glioblastoma progression, thereby laying a framework to unveil targetable metabolic vulnerabilities in glioblastoma.

Team players in the pathogenesis of metabolic dysfunctions-associated steatotic liver disease: The basis of development of pharmacotherapy

Nutrient metabolism is regulated by several factors. Social determinants of health with or without genetics are the primary regulator of metabolism, and an unhealthy lifestyle affects all modulators and mediators, leading to the adaptation and finally to the exhaustion of cellular functions. Hepatic steatosis is defined by presence of fat in more than 5% of hepatocytes. In hepatocytes, fat is stored as triglycerides in lipid droplet. Hepatic steatosis results from a combination of multiple intracellular processes. In a healthy individual nutrient metabolism is regulated at several steps. It ranges from the selection of nutrients in a grocery store to the last step of consumption of ATP as an energy or as a building block of a cell as structural component. Several hormones, peptides, and genes have been described that participate in nutrient metabolism. Several enzymes participate in each nutrient metabolism as described above from ingestion to generation of ATP. As of now several publications have revealed very intricate regulation of nutrient metabolism, where most of the regulatory factors are tied to each other bidirectionally, making it difficult to comprehend chronological sequence of events. Insulin hormone is the primary regulator of all nutrients' metabolism both in prandial and fasting states. Insulin exerts its effects directly and indirectly on enzymes involved in the three main cellular function processes; metabolic, inflammation and repair, and cell growth and regeneration. Final regulators that control the enzymatic functions through stimulation or suppression of a cell are nuclear receptors in especially farnesoid X receptor and peroxisome proliferator-activated receptor/RXR ligands, adiponectin, leptin, and adiponutrin. Insulin hormone has direct effect on these final modulators. Whereas blood glucose level, serum lipids, incretin hormones, bile acids in conjunction with microbiota are intermediary modulators which are controlled by lifestyle. The purpose of this review is to overview the key players in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) that help us understand the disease natural course, risk stratification, role of lifestyle and pharmacotherapy in each individual patient with MASLD to achieve personalized care and target the practice of precision medicine. PubMed and Google Scholar databases were used to identify publication related to metabolism of carbohydrate and fat in states of health and disease states; MASLD, cardiovascular disease and cancer. More than 1000 publications including original research and review papers were reviewed.

B3galt5 functions as a PXR target gene and regulates obesity and insulin resistance by maintaining intestinal integrity

Pregnane X receptor (PXR) has been reported to regulate glycolipid metabolism. The dysfunction of intestinal barrier contributes to metabolic disorders. However, the role of intestinal PXR in metabolic diseases remains largely unknown. Here, we show that activation of PXR by tributyl citrate (TBC), an intestinal-selective PXR agonist, improves high fat diet (HFD)-induced obesity. The metabolic benefit of intestinal PXR activation is associated with upregulation of β-1,3 galactosyltransferase 5 (B3galt5). Our results reveal that B3galt5 mainly expresses in the intestine and is a direct PXR transcriptional target. B3galt5 knockout exacerbates HFD-induced obesity, insulin resistance and inflammation. Mechanistically, B3galt5 is essential to maintain the integrity of intestinal mucus barrier. B3galt5 ablation impairs the O-glycosylation of mucin2, destabilizes the mucus layer, and increases intestinal permeability. Furthermore, B3galt5 deficiency abolishes the beneficial effect of intestinal PXR activation on metabolic disorders. Our results suggest the intestinal-selective PXR activation regulates B3galt5 expression and maintains metabolic homeostasis, making it a potential therapeutic strategy in obesity.

Metabolomics reveals dysregulated all-trans retinoic acid and polyunsaturated fatty acid metabolism contribute to PXR-induced hepatic steatosis in mice

Activation of pregnane X receptor (PXR) by xenobiotics has been associated with metabolic diseases. This study aimed to reveal the impact of PXR activation on hepatic metabolome and explore novel mechanisms underlying PXR-mediated lipid metabolism disorder in the liver. Wild-type and PXR-deficient male C57BL/6 mice were used as in vivo models, and hepatic steatosis was induced by pregnenolone-16α-carbonitrile, a typical rodent PXR agonist. Metabolomic analysis of liver tissues showed that PXR activation led to significant changes in metabolites involved in multiple metabolic pathways previously reported, including lipid metabolism, energy homeostasis, and amino acid metabolism. Moreover, the level of hepatic all-trans retinoic acid (ATRA), the main active metabolite of vitamin A, was significantly increased by PXR activation, and genes involved in ATRA metabolism exhibited differential expression following PXR activation or deficiency. Consistent with previous research, the expression of downstream target genes of peroxisome proliferator-activated receptor α (PPARα) was decreased. Analysis of fatty acids by Gas Chromatography-Mass Spectrometer further revealed changes in polyunsaturated fatty acid metabolism upon PXR activation, suggesting inhibition of PPARα activity. Taken together, our findings reveal a novel metabolomic signature of hepatic steatosis induced by PXR activation in mice.

Metabolic flux in macrophages in obesity and type-2 diabetes

Recent literature extensively investigates the crucial role of energy metabolism in determining the inflammatory response and polarization status of macrophages. This rapidly expanding area of research highlights the importance of understanding the link between energy metabolism and macrophage function. The metabolic pathways in macrophages are intricate and interdependent, and they can affect the polarization of macrophages. Previous studies suggested that glucose flux through cytosolic glycolysis is necessary to trigger pro-inflammatory phenotypes of macrophages, and fatty acid oxidation is crucial to support anti-inflammatory responses. However, recent studies demonstrated that this understanding is oversimplified and that the metabolic control of macrophage polarization is highly complex and not fully understood yet. How the metabolic flux through different metabolic pathways (glycolysis, glucose oxidation, fatty acid oxidation, ketone oxidation, and amino acid oxidation) is altered by obesity- and type 2 diabetes (T2D)-associated insulin resistance is also not fully defined. This mini-review focuses on the impact of insulin resistance in obesity and T2D on the metabolic flux through the main metabolic pathways in macrophages, which might be linked to changes in their inflammatory responses. We closely evaluated the experimental studies and methodologies used in the published research and highlighted priority research areas for future investigations.

Synergistic Steatosis Induction in Mice: Exploring the Interactions and Underlying Mechanisms between PFOA and Tributyltin

This study explores the impact of environmental pollutants on nuclear receptors (CAR, PXR, PPARα, PPARγ, FXR, and LXR) and their heterodimerization partner, the Retinoid X Receptor (RXR). Such interaction may contribute to the onset of non-alcoholic fatty liver disease (NAFLD), which is initially characterized by steatosis and potentially progresses to steatohepatitis and fibrosis. Epidemiological studies have linked NAFLD occurrence to the exposure to environmental contaminants like PFAS. This study aims to assess the simultaneous activation of nuclear receptors via perfluorooctanoic acid (PFOA) and RXR coactivation via Tributyltin (TBT), examining their combined effects on steatogenic mechanisms. Mice were exposed to PFOA (10 mg/kg/day), TBT (5 mg/kg/day) or a combination of them for three days. Mechanisms underlying hepatic steatosis were explored by measuring nuclear receptor target gene and lipid metabolism key gene expressions, by quantifying plasma lipids and hepatic damage markers. This study elucidated the involvement of the Liver X Receptor (LXR) in the combined effect on steatosis and highlighted the permissive nature of the LXR/RXR heterodimer. Antagonistic effects of TBT on the PFOA-induced activation of the Pregnane X Receptor (PXR) and Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) were also observed. Overall, this study revealed complex interactions between PFOA and TBT, shedding light on their combined impact on liver health.

Germ-free status but not subacute polychlorinated biphenyl (PCB) exposure altered hepatic phosphatidylcholine and ether-phosphatidylcholine levels in mice

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that pose a current ecosystem and human health concern. PCB exposure impacts the gut microbiome in animal models, suggesting a mechanistic link between PCB exposure and adverse health outcomes. The presence and absence of the microbiome and exposure to PCBs independently affect the lipid composition in the liver, which in turn affects the PCB disposition in target tissues, such as the liver. Here, we investigated microbiome × subacute PCB effects on the hepatic lipid composition of conventional and germ-free female mice exposed to 0, 6, or 30 mg/kg body weight of an environmental PCB mixture in sterile corn oil once daily for 3 consecutive days. Hepatic triacylglyceride and polar lipid levels were quantified using mass spectrometric methods following the subacute PCB exposure. The lipidomic analysis revealed no PCB effect on the hepatic levels. No microbiome effect was observed on levels of triacylglyceride and most polar lipid classes. The total hepatic levels of phosphatidylcholine (PC) and ether-phosphatidylcholine (ePC) lipids were lower in germ-free mice than the conventional mice from the same exposure group. Moreover, levels of several unsaturated PCs, such as PC(36:5) and PC(42:10), and ePCs, such as ePC(36:2) and ePC(4:2), were lower in germ-free than conventional female mice. Based on a KEGG pathway meta-analysis of RNA sequencing data, the ether lipid metabolism pathway is altered in the germ-free mouse liver. In contrast to the liver, extractable lipid levels, determined gravimetrically, differed in several tissues from naïve conventional vs. germ-free mice. Overall, microbiome × subacute PCB exposure effects on hepatic lipid composition are unlikely to affect PCB distribution into the mouse liver. Further studies are needed to assess how the different extractable lipid levels in other tissues alter PCB distribution in conventional vs. germ-free mice.

Targeting liver and adipose tissue in obese mice: Effects of a N-acylethanolamine mixture on insulin resistance and adipocyte reprogramming

N-acylethanolamines (NAEs) are endogenous lipid-signalling molecules involved in inflammation and energy metabolism. The potential pharmacological effect of NAE association in managing inflammation-based metabolic disorders is unexplored. To date, targeting liver-adipose axis can be considered a therapeutic approach for the treatment of obesity and related dysfunctions. Here, we investigated the metabolic effect of OLALIAMID® (OLA), an olive oil-derived NAE mixture, in limiting liver and adipose tissue (AT) dysfunction of high-fat diet (HFD)-fed mice. OLA reduced body weight and fat mass in obese mice, decreasing insulin resistance (IR), as shown by homeostasis model assessment index, and leptin/adiponectin ratio, a marker of adipocyte dysfunction. OLA improved serum lipid and hepatic profile and the immune/inflammatory pattern of metainflammation. In liver of HFD mice, OLA treatment counteracted glucose and lipid dysmetabolism, restoring insulin signalling (phosphorylation of AKT and AMPK), and reducing mRNAs of key markers of fatty acid accumulation. Furthermore, OLA positively affected AT function deeply altered by HFD by reprogramming of genes involved in thermogenesis of interscapular brown AT (iBAT) and subcutaneous white AT (scWAT), and inducing the beigeing of scWAT. Notably, the NAE mixture reduced inflammation in iBAT and promoted M1-to-M2 macrophage shift in scWAT of obese mice. The tissue and systemic anti-inflammatory effects of OLA and the increased expression of glucose transporter 4 in scWAT contributed to the improvement of gluco-lipid toxicity and insulin sensitivity. In conclusion, we demonstrated that this olive oil-derived NAE mixture is a valid nutritional strategy to counteract IR and obesity acting on liver-AT crosstalk, restoring both hepatic and AT function and metabolism.

Liver X receptor agonist upregulates LPCAT3 in human aortic endothelial cells

Objective

Endothelial cells (ECs) play an important role in tissue homeostasis. Recently, EC lipid metabolism has emerged as a regulator of EC function. The liver X receptors (LXRs) are involved in the transcriptional regulation of genes involved in lipid metabolism and have been identified as a potential target in cardiovascular disease. We aimed to decipher the role of LXRs in the regulation of lipid metabolism in human aortic endothelial cells.

Approach and Results

Lipid composition analysis of endothelial cells treated with the LXR agonist T0901317 revealed that LXR activation increased the proportion of polyunsaturated fatty acids (PUFAs) and decreased the proportion of saturated fatty acids. The LXR agonist decreased the uptake of fatty acids (FAs) by ECs. This effect was abolished by LXRα silencing. LXR activation increased the activity and the expression of lysophosphatidylcholine acyltransferase, LPCAT3, which is involved in the turnover of FAs at the sn-2 position of phospholipids. Transcriptomic analysis also revealed that LXRs increased the expression of key genes involved in the synthesis of PUFAs, including FA desaturase one and 2, FA elongase 5 and fatty acid synthase. Subsequently, the LXR agonist increased PUFA synthesis and enhanced arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid content in the EC phospholipids. Modification of the FA composition of ECs by LXRs led to a decrease of arachidonate and linoleate derived prostaglandins synthesis and release. No change on markers of inflammation induced by plasma from sickle cell patient were observed in presence of LXR agonist.

Conclusion

These results identify LXR as a key regulator of lipid metabolism in human aortic endothelial cells and a direct effect of LXR agonist on lysophosphatidylacyl transferase (LPCAT3).

BMAL1 deletion protects against obesity and non-alcoholic fatty liver disease induced by a high-fat diet

OBJECTIVES

Obesity and non-alcoholic fatty liver disease (NAFLD) are major health concerns. The circadian rhythm is an autonomous and intrinsic timekeeping system closely associated with energy metabolism and obesity. Thus, this study explored the role of brain and muscle aryl hydrocarbon receptor nuclear translocator-like1 (BMAL1), a circadian clock regulator, in the development of obesity and NAFLD.

METHODS

We generated BMAL1 knockout (BMAL1 KO) mice to imitate circadian rhythm disruption. The study comprised three groups from the same litter: BMAL1 KO mice fed a high-fat diet (to establish obesity and NAFLD phenotypes), wild-type mice fed normal chow, and wild-type mice fed a high-fat diet. The metabolic and NAFLD phenotypes were assessed via physiological measurements and histological examinations. Quantitative polymerase chain reaction and western blotting were used to identify and validate changes in the signaling pathways responsible for the altered NAFLD phenotypes in the wild-type and BMAL1 KO mice.

RESULTS

BMAL1 depletion protected against obesity and metabolic disorders induced by a high-fat diet. BMAL1 depletion also prevented hepatic steatosis and inhibited cluster of differentiation 36 and peroxisome proliferator-activated receptor gamma (i.e., PPARγ) expression.

CONCLUSIONS

BMAL1 plays an important role in the development of obesity and NAFLD and, thus, is a potential therapeutic target for these conditions.

CD36 as a gatekeeper of myocardial lipid metabolism and therapeutic target for metabolic disease

The multifunctional membrane glycoprotein CD36 is expressed in different types of cells and plays a key regulatory role in cellular lipid metabolism, especially in cardiac muscle. CD36 facilitates the cellular uptake of long-chain fatty acids, mediates lipid signaling, and regulates storage and oxidation of lipids in various tissues with active lipid metabolism. CD36 deficiency leads to marked impairments in peripheral lipid metabolism, which consequently impact on the cellular utilization of multiple different fuels because of the integrated nature of metabolism. The functional presence of CD36 at the plasma membrane is regulated by its reversible subcellular recycling from and to endosomes and is under the control of mechanical, hormonal, and nutritional factors. Aberrations in this dynamic role of CD36 are causally associated with various metabolic diseases, in particular insulin resistance, diabetic cardiomyopathy, and cardiac hypertrophy. Recent research in cardiac muscle has disclosed the endosomal proton pump vacuolar-type H+-ATPase (v-ATPase) as a key enzyme regulating subcellular CD36 recycling and being the site of interaction between various substrates to determine cellular substrate preference. In addition, evidence is accumulating that interventions targeting CD36 directly or modulating its subcellular recycling are effective for the treatment of metabolic diseases. In conclusion, subcellular CD36 localization is the major adaptive regulator of cellular uptake and metabolism of long-chain fatty acids and appears a suitable target for metabolic modulation therapy to mend failing hearts.

Research status and hotspots on the mechanisms of liver X receptor in cancer progression: A bibliometric analysis

BACKGROUND

The mechanism of liver X receptor in cancer has been gradually revealed in recent years. This study is committed to analyzing the current research status of the mechanism of liver × receptor in cancer progression by using bibliometric methods and to explore the development trend of liver × receptor related research in the future, in order to provide some reference for further exploration in this field.

METHODS

The Web of Science core collection database was used to carry out the original data retrieval. Excel software was used for data statistics. Vosviewer and CiteSpace software were used to analyze the publication situation, cooperation network, reference co-citation, keyword and term co-occurrence, term bursts, and cluster analysis, and draw visual maps.

RESULTS

A total of 631 publications meeting the research criteria were included by December 2022, with an average of 32.5 citations per paper. The main research fields were molecular biology, oncology and cell biology, and the papers were mainly published in journals about molecular, biology and immunology. Cell is the journal with the highest citation. The United States is the most influential country, the University of California, Los Angeles is the main research institution, and Gustafsson, Jan-ake is the author with the highest output. In reference co-citation clustering, cluster#2 "cancer development" is the main cluster, and the period from 2014 to 2018 is an important stage of relevant theoretical progress. "Tumor microenvironment" with high burst and novelty became the most noteworthy term in term burst.

CONCLUSION

Using bibliometric methods to reveal the current status of LXR and cancer mechanisms, and making predictions of possible future hotspots based on the analysis of the current situation, the translation of LXR anti-cancer research to clinical applications, the impact on the tumor microenvironment as a whole and more immune pathways, and the formation of a systematic cognition of the effects of more cancer cell lines and oncogenic signaling crosstalk, which is a possible direction for future research.

Diarrhea induced by insufficient fat absorption in weaned piglets: Causes and nutrition regulation

Fat is one of the three macronutrients and a significant energy source for piglets. It plays a positive role in maintaining intestinal health and improving production performance. During the weaning period, physiological, stress and diet-related factors influence the absorption of fat in piglets, leading to damage to the intestinal barrier, diarrhea and even death. Signaling pathways, such as fatty acid translocase (CD36), pregnane X receptor (PXR), and AMP-dependent protein kinase (AMPK), are responsible for regulating intestinal fat uptake and maintaining intestinal barrier function. Therefore, this review mainly elaborates on the reasons for diarrhea induced by insufficient fat absorption and related signaling pathways in weaned-piglets, with an emphasis on the intestinal fat absorption disorder. Moreover, we focus on introducing nutritional strategies that can promote intestinal fat absorption in piglets with insufficient fat absorption-related diarrhea, such as lipase, amino acids, and probiotics.

Targeting nuclear receptors for NASH/MASH: From bench to bedside

The onset of metabolic dysfunction-associated steatohepatitis (MASH) or non-alcoholic steatohepatitis (NASH) represents a tipping point leading to liver injury and subsequent hepatic complications in the natural progression of what is now termed metabolic dysfunction-associated steatotic liver diseases (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD). With no pharmacological treatment currently available for MASH/NASH, the race is on to develop drugs targeting multiple facets of hepatic metabolism, inflammation, and pro-fibrotic events, which are major drivers of MASH. Nuclear receptors (NRs) regulate genomic transcription upon binding to lipophilic ligands and govern multiple aspects of liver metabolism and inflammation. Ligands of NRs may include hormones, lipids, bile acids, and synthetic ligands, which upon binding to NRs regulate the transcriptional activities of target genes. NR ligands are presently the most promising drug candidates expected to receive approval from the United States Food and Drug Administration as a pharmacological treatment for MASH. This review aims to cover the current understanding of NRs, including nuclear hormone receptors, non-steroid hormone receptors, circadian NRs, and orphan NRs, which are currently undergoing clinical trials for MASH treatment, along with NRs that have shown promising results in preclinical studies.

Dock5 Deficiency Promotes Proteinuric Kidney Diseases via Modulating Podocyte Lipid Metabolism

Podocytes are particularly sensitive to lipid accumulation, which has recently emerged as a crucial pathological process in the progression of proteinuric kidney diseases like diabetic kidney disease and focal segmental glomerulosclerosis. However, the underlying mechanism remains unclear. Here, podocytes predominantly expressed protein dedicator of cytokinesis 5 (Dock5) is screened to be critically related to podocyte lipid lipotoxicity. Its expression is reduced in both proteinuric kidney disease patients and mouse models. Podocyte-specific deficiency of Dock5 exacerbated podocyte injury and glomeruli pathology in proteinuric kidney disease, which is mainly through modulating fatty acid uptake by the liver X receptor α  (LXRα)/scavenger receptor class B (CD36) signaling pathway. Specifically, Dock5 deficiency enhanced CD36-mediated fatty acid uptake of podocytes via upregulating LXRα in an m6 A-dependent way. Moreover, the rescue of Dock5 expression ameliorated podocyte injury and proteinuric kidney disease. Thus, the findings suggest that Dock5 deficiency is a critical contributor to podocyte lipotoxicity and may serve as a promising therapeutic target in proteinuric kidney diseases.

Metabolic effects of nuclear receptor activation in vivo after 28-day oral exposure to three endocrine-disrupting chemicals

Environmental exposure to endocrine-disrupting chemicals (EDCs) can lead to metabolic disruption, resulting in metabolic complications including adiposity, dyslipidemia, hepatic lipid accumulation, and glucose intolerance. Hepatic nuclear receptor activation is one of the mechanisms mediating metabolic effects of EDCs. Here, we investigated the potential to use a repeated dose 28-day oral toxicity test for identification of EDCs with metabolic endpoints. Bisphenol A (BPA), pregnenolone-16α-carbonitrile (PCN), and perfluorooctanoic acid (PFOA) were used as reference compounds. Male and female wild-type C57BL/6 mice were orally exposed to 5, 50, and 500 μg/kg of BPA, 1000, 10 000, and 100 000 µg/kg of PCN and 50 and 300 μg/kg of PFOA for 28 days next to normal chow diet. Primary endpoints were glucose tolerance, hepatic lipid accumulation, and plasma lipids. After 28-day exposure, no changes in body weight and glucose tolerance were observed in BPA-, PCN-, or PFOA-treated males or females. PCN and PFOA at the highest dose in both sexes and BPA at the middle and high dose in males increased relative liver weight. PFOA reduced plasma triglycerides in males and females, and increased hepatic triglyceride content in males. PCN and PFOA induced hepatic expression of typical pregnane X receptor (PXR) and peroxisome proliferator-activated receptor (PPAR)α target genes, respectively. Exposure to BPA resulted in limited gene expression changes. In conclusion, the observed changes on metabolic health parameters were modest, suggesting that a standard repeated dose 28-day oral toxicity test is not a sensitive method for the detection of the metabolic effect of EDCs.

9-HODE and 9-HOTrE alter mitochondrial metabolism, increase triglycerides, and perturb fatty acid uptake and synthesis associated gene expression in HepG2 cells

Non-Alcoholic Fatty Liver Disease (NAFLD) prevalence is rising and can lead to detrimental health outcomes such as Non-Alcoholic Steatohepatitis (NASH), cirrhosis, and cancer. Recent studies have indicated that Cytochrome P450 2B6 (CYP2B6) is an anti-obesity CYP in humans and mice. Cyp2b-null mice are diet-induced obese, and human CYP2B6-transgenic (hCYP2B6-Tg) mice reverse the obesity or diabetes progression, but with increased liver triglyceride accumulation in association with an increase of several oxylipins. Notably, 9-hydroxyoctadecadienoic acid (9-HODE) produced from linoleic acid (LA, 18:2, ω-6) is the most prominent of these and 9-hydroxyoctadecatrienoic acid (9-HOTrE) from alpha-linolenic acid (ALA, 18:3, ω-3) is the most preferentially produced when controlling for substrate concentrations in vitro. Transactivation assays indicate that 9-HODE and 9-HOTrE activate PPARα and PPARγ. In Seahorse assays performed in HepG2 cells, 9-HOTrE increased spare respiratory capacity, slightly decreased palmitate metabolism, and increased non-glycolytic acidification in a manner consistent with slightly increased glutamine utilization; however, 9-HODE exhibited no effect on metabolism. Both compounds increased triglyceride and pyruvate concentrations, most strongly by 9-HOTrE, consistent with increased spare respiratory capacity. qPCR analysis revealed several perturbations in fatty acid uptake and metabolism gene expression. 9-HODE increased expression of CD36, FASN, PPARγ, and FoxA2 that are involved in lipid uptake and production. 9-HOTrE decreased ANGPTL4 expression and increased FASN expression consistent with increased fatty acid uptake, fatty acid production, and AMPK activation. Our findings support the hypothesis that 9-HODE and 9-HOTrE promote steatosis, but through different mechanisms as 9-HODE is directly involved in fatty acid uptake and synthesis; 9-HOTrE weakly inhibits mitochondrial fatty acid metabolism while increasing glutamine use.

The regulatory role of CD36 in hematopoiesis beyond fatty acid uptake

CD36 is a transmembrane glycoprotein, located on surface of numerous cell types. This review is aimed to explore regulatory role of CD36 in hematopoiesis beyond fatty acid uptake. CD36 acts as a pattern recognition receptor, regulates cellular fatty acid homeostasis, and negatively monitors angiogenesis. CD36 also mediates free fatty acid transportation to hematopoietic stem cells in response to infections. During normal physiology and pathophysiology, CD36 significantly participates in the activation and metabolic needs of platelets, macrophages, monocytes, T cells, B cells, and dendritic cells. CD36 has shown a unique relationship with Plasmodium falciparum-infected erythrocytes (PfIEs) as a beneficiary for both parasite and host. CD36 actively participates in pathogenesis of various hematological cancers as a significant prognostic biomarker including AML, HL, and NHL. CD36-targeting antibodies, CD36 antagonists (small molecules), and CD36 expression inhibitors/modulators are used to target CD36, depicting its therapeutic potential. Many preclinical studies or clinical trials were performed to assess CD36 as a therapeutic target; some are still under investigation. This review reflects the role of CD36 in hematopoiesis which requires more consideration in future research.

Nonalcoholic Fatty Liver Disease Development in Male Mice upon Exposure to Flubendiamide

Flubendiamide (FLU), a widely used diamide insecticide, has been observed to potentiate adipogenesis in 3T3-L1 preadipocytes in vitro. Whether exposure to FLU disrupts hepatic lipid homeostasis in mammals and induces visceral obesity, however, remains unclear. The aim of this study was to assess the effects of FLU when administered orally to male C57BL/6J mice under normal diet (ND) and high-fat diet (HFD) conditions. FLU accumulated at higher levels in the tissues of the HFD group than those of the ND group, indicating that an HFD contributed to the accumulation of lipophilic pesticides in vivo. Notably, FLU (logP = 4.14) is highly lipophilic and easily accumulates in fat. Exposure to FLU had opposing effects on the lipid metabolism of the liver in the ND and HFD groups. Liver triacylglycerol levels in the ND group were reduced, while those in the HFD group were increased, resulting in more severe hepatic steatosis. More lipid accumulation was also observed in HepG2 cells exposed to FLU. Changes in hepatic lipid deposition in vivo occurred as the enhanced transcriptional regulation of the genes involved in lipid uptake, de novo lipogenesis, and fatty acid β-oxidation (FAO). Moreover, an excessive increase in FAO caused oxidative stress, which in turn exacerbated the inflammation of the liver. This study revealed the disruptive effect of FLU exposure on hepatic lipid homeostasis, which may facilitate the triggering of nonalcoholic fatty liver disease in HFD-fed mice.

Functional role of Ash2l in oxLDL induced endothelial dysfunction and atherosclerosis

Endothelial injury and dysfunction in the artery wall fuel the process of atherosclerosis. As a key epigenetic regulator, Ash2l (Absent, small, or homeotic-Like 2) is involved in regulating vascular injury and its complications. However, the role of Ash2l in atherosclerosis has not yet been fully elucidated. Here, we found increased Ash2l expression in high-cholesterol diet-fed ApoE-/- mice and oxidized LDL (oxLDL) treated endothelial cells (ECs). Furthermore, Ash2l promoted the scavenger receptors transcription by catalyzing histone H3 lysine 4 (H3K4) trimethylation at the promoter region of transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) and triggered the activation of the pro-inflammatory nuclear factor-kappa B (NF-κB) by enhancing interaction between CD36 and toll-like receptor 4 (TLR4). Meanwhile, enhanced expression of scavenger receptors drove more oxLDL uptake by ECs. In vivo studies revealed that ECs-specific Ash2l knockdown reduced atherosclerotic lesion formation and promoted fibrous cap stability in the aorta of ApoE-/- mice, which was partly associated with a reduced endothelial activation by suppressing scavenger receptors and the uptake of lipids by ECs. Collectively, our findings identify Ash2l as a novel regulator that mediates endothelial injury and atherosclerosis. Targeting Ash2l may provide valuable insights for developing novel therapeutic candidates for atherosclerosis.

Pinuseldarone, a Clerodane-Type Diterpene from Pinus eldarica Needles and Phytochemicals as Novel Agents for Regulating Brown Adipogenesis and Thermogenesis

Phytochemical investigation of the MeOH extract of Pinus eldarica needles led to the isolation and identification of a new clerodane-type diterpene, pinuseldarone (1), along with a known flavonoid, 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone (2), through HPLC purification. The structure of the new compound 1 was elucidated using spectroscopic methods, including 1D and 2D NMR, as well as HRESIMS. Its absolute configuration was established through NOESY analysis and computational methods, including electronic circular dichroism (ECD) calculations and gauge-including atomic orbital NMR chemical shift calculations, followed by DP4+ probability analysis. The metabolic implications of the isolated compounds were assessed using a cultured brown adipocyte model derived from murine brown adipose tissue. It was observed that treatment with dihydroxy-3,7,8-trimethoxy-6-C-methylflavone (2) downregulates the adipogenic marker C/EBPδ and fatty acid transporter CD36, resulting in a significant reduction in lipid accumulation during brown adipocyte differentiation. However, pinuseldarone (1) treatment did not affect brown adipocyte differentiation. Interestingly, pretreatment with pinuseldarone (1) potentiated the pharmacological stimulation of brown adipocytes, seemingly achieved by sensitizing their response to β3-adrenoreceptor signaling. Therefore, our findings indicate that phytochemicals derived from P. eldarica needles could potentially serve as valuable compounds for adjusting the metabolic activity of brown adipose tissue, a vital component in maintaining whole-body metabolic homeostasis.

Regulation of PXR in drug metabolism: chemical and structural perspectives

INTRODUCTION

Pregnane X receptor (PXR) is a master xenobiotic sensor that transcriptionally controls drug metabolism and disposition pathways. PXR activation by pharmaceutical drugs, natural products, environmental toxins, etc. may decrease drug efficacy and increase drug-drug interactions and drug toxicity, indicating a therapeutic value for PXR antagonists. However, PXR's functions in physiological events, such as intestinal inflammation, indicate that PXR activators may be useful in certain disease contexts.

AREAS COVERED

We review the reported roles of PXR in various physiological and pathological processes including drug metabolism, cancer, inflammation, energy metabolism, and endobiotic homeostasis. We then highlight specific cellular and chemical routes that modulate PXR activity and discuss the functional consequences. Databases searched and inclusive dates: PubMed, 1 January 1980 to 10 January 2024.

EXPERT OPINION

Knowledge of PXR's drug metabolism function has helped drug developers produce small molecules without PXR-mediated metabolic liabilities, and further understanding of PXR's cellular functions may offer drug development opportunities in multiple disease settings.

Cultivated Enterococcus faecium B6 from children with obesity promotes nonalcoholic fatty liver disease by the bioactive metabolite tyramine

Gut microbiota plays an essential role in nonalcoholic fatty liver disease (NAFLD). However, the contribution of individual bacterial strains and their metabolites to childhood NAFLD pathogenesis remains poorly understood. Herein, the critical bacteria in children with obesity accompanied by NAFLD were identified by microbiome analysis. Bacteria abundant in the NAFLD group were systematically assessed for their lipogenic effects. The underlying mechanisms and microbial-derived metabolites in NAFLD pathogenesis were investigated using multi-omics and LC-MS/MS analysis. The roles of the crucial metabolite in NAFLD were validated in vitro and in vivo as well as in an additional cohort. The results showed that Enterococcus spp. was enriched in children with obesity and NAFLD. The patient-derived Enterococcus faecium B6 (E. faecium B6) significantly contributed to NAFLD symptoms in mice. E. faecium B6 produced a crucial bioactive metabolite, tyramine, which probably activated PPAR-γ, leading to lipid accumulation, inflammation, and fibrosis in the liver. Moreover, these findings were successfully validated in an additional cohort. This pioneering study elucidated the important functions of cultivated E. faecium B6 and its bioactive metabolite (tyramine) in exacerbating NAFLD. These findings advance the comprehensive understanding of NAFLD pathogenesis and provide new insights for the development of microbe/metabolite-based therapeutic strategies.

Early-life stress perturbs the epigenetics of Cd36 concurrent with adult onset of NAFLD in mice

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases in the U.S. and worldwide. The roles of early postnatal life stress (EPLS) and the fatty acid translocase (CD36) on the pathogenesis of adult-onset NAFLD remain unknown. We hypothesized that EPLS, in the form of neonatal maternal separation (NMS), would predispose mice towards developing adult NAFLD, increase hepatic CD36 expression, and differentially methylate Cd36 promoter concurrently.

METHODS

NMS was performed on mice from postnatal day 1 to 21 and a high-fat/high-sucrose (HFS) diet was started at 4 weeks of age to generate four experimental groups: Naive-control diet (CD), Naive-HFS, NMS-CD, and NMS-HFS.

RESULTS

NMS alone caused NAFLD in adult male mice at 25 weeks of age. The effects of NMS and HFS were generally additive in terms of NAFLD, hepatic Cd36 mRNA levels, and hepatic Cd36 promoter DNA hypomethylation. Cd36 promoter methylation negatively correlated with Cd36 mRNA levels. Two differentially methylated regions (DMRs) within Cd36 promoter regions appeared to be vulnerable to NMS in the mouse.

CONCLUSIONS

Our findings suggest that NMS increases the risk of an individual, particularly male, towards NAFLD when faced with a HFS diet later in life.

IMPACT

The key message of this article is that neonatal maternal separation and a postweaning high-fat/high-sucrose diet increased the risk of an individual, particularly male, towards NAFLD in adult life. What this study adds to the existing literature includes the identification of two vulnerable differentially methylated regions in hepatic Cd36 promoters whose methylation levels very strongly negatively correlated with Cd36 mRNA. The impact of this article is that it provides an early-life environment-responsive gene/promoter methylation model and an animal model for furthering the mechanistic study on how the insults in early-life environment are "transmitted" into adulthood and caused NAFLD.

AhR, PXR and CAR: From Xenobiotic Receptors to Metabolic Sensors

Traditionally, xenobiotic receptors are known for their role in chemical sensing and detoxification, as receptor activation regulates the expression of various key enzymes and receptors. However, recent studies have highlighted that xenobiotic receptors also play a key role in the regulation of lipid metabolism and therefore function also as metabolic sensors. Since dyslipidemia is a major risk factor for various cardiometabolic diseases, like atherosclerosis and non-alcoholic fatty liver disease, it is of major importance to understand the molecular mechanisms that are regulated by xenobiotic receptors. In this review, three major xenobiotic receptors will be discussed, being the aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). Specifically, this review will focus on recent insights into the metabolic functions of these receptors, especially in the field of lipid metabolism and the associated dyslipidemia.

Drug screen identifies verteporfin as a regulator of lipid metabolism in macrophage foam cells

Arterial macrophage foam cells are filled with cholesterol ester (CE) stored in cytosolic lipid droplets (LDs). Foam cells are central players in progression of atherosclerosis as regulators of lipid metabolism and inflammation, two major driving forces of atherosclerosis development. Thus, foam cells are considered plausible targets for intervention in atherosclerosis. However, a compound that directly regulates the lipid metabolism of LDs in the arterial foam cells has not yet been identified. In this study, we screened compounds that inhibit macrophage foam cell formation using a library of 2697 FDA-approved drugs. From the foam cells generated via loading of human oxidized low-density lipoprotein (oxLDL), we found 21 and 6 compounds that reduced and enhanced accumulations of lipids respectively. Among them, verteporfin most significantly reduced oxLDL-induced foam cell formation whereas it did not display a significant impact on foam cell formation induced by fatty acid. Mechanistically our data demonstrate that verteporfin acts via inhibition of oxLDL association with macrophages, reducing accumulation of CE. Interestingly, while other drugs that reduced foam cell formation did not have impact on pre-existing foam cells, verteporfin treatment significantly reduced their total lipids, CE, and pro-inflammatory gene expression. Together, our study identifies verteporfin as a novel regulator of foam cell lipid metabolism and inflammation and a potential compound for intervention in atherosclerosis.

Mechanisms of Lipid Droplet Accumulation in Steatotic Liver Diseases

The steatotic diseases of metabolic dysfunction-associated steatotic liver disease (MASLD), alcohol-associated liver disease (ALD), and chronic hepatitis C (HCV) account for the majority of liver disease prevalence, morbidity, and mortality worldwide. While these diseases have distinct pathogenic and clinical features, dysregulated lipid droplet (LD) organelle biology represents a convergence of pathogenesis in all three. With increasing understanding of hepatocyte LD biology, we now understand the roles of LD proteins involved in these diseases but also how genetics modulate LD biology to either exacerbate or protect against the phenotypes associated with steatotic liver diseases. Here, we review the history of the LD organelle and its biogenesis and catabolism. We also review how this organelle is critical not only for the steatotic phenotype of liver diseases but also for their advanced phenotypes. Finally, we summarize the latest attempts and challenges of leveraging LD biology for therapeutic gain in steatotic diseases. In conclusion, the study of dysregulated LD biology may lead to novel therapeutics for the prevention of disease progression in the highly prevalent steatotic liver diseases of MASLD, ALD, and HCV.

Intermittent Fasting Attenuates Metabolic-Dysfunction-Associated Steatohepatitis by Enhancing the Hepatic Autophagy-Lysosome Pathway

An intermittent fasting (IF) regimen has been shown to protect against metabolic dysfunction-associated steatohepatitis (MASH). However, the precise mechanism remains unclear. Here, we explored how IF reduced hepatic lipid accumulation, inflammation, and fibrosis in mice with MASH. The mice were fed a high-fat diet (HFD) for 30 weeks and either continued on the HFD or were subjected to IF for the final 22 weeks. IF reduced body weight, insulin resistance, and hepatic lipid accumulation in HFD-fed mice. Lipidome analysis revealed that IF modified HFD-induced hepatic lipid composition. In particular, HFD-induced impaired autophagic flux was reversed by IF. The decreased hepatic lysosome-associated membrane protein 1 level in HFD-fed mice was upregulated in HFD+IF-fed mice. However, increased hepatic lysosomal acid lipase protein levels in HFD-fed mice were reduced by IF. IF attenuated HFD-induced hepatic inflammation and galectin-3-positive Kupffer cells. In addition to the increases in hepatic hydroxyproline and lumican levels, lipocalin-2-mediated signaling was reversed in HFD-fed mice by IF. Taken together, our findings indicate that the enhancement of the autophagy-lysosomal pathway may be a critical mechanism of MASH reduction by IF.

Molecular mechanisms of metabolic disease-associated hepatic inflammation in non-alcoholic fatty liver disease and non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide, with a progressive form of non-alcoholic steatohepatitis (NASH). It may progress to advanced liver diseases, including liver fibrosis, cirrhosis, and hepatocellular carcinoma. NAFLD/NASH is a comorbidity of many metabolic disorders such as obesity, insulin resistance, type 2 diabetes, cardiovascular disease, and chronic kidney disease. These metabolic diseases are often accompanied by systemic or extrahepatic inflammation, which plays an important role in the pathogenesis and treatment of NAFLD or NASH. Metabolites, such as short-chain fatty acids, impact the function, inflammation, and death of hepatocytes, the primary parenchymal cells in the liver tissue. Cholangiocytes, the epithelial cells that line the bile ducts, can differentiate into proliferative hepatocytes in chronic liver injury. In addition, hepatic non-parenchymal cells, including liver sinusoidal endothelial cells, hepatic stellate cells, and innate and adaptive immune cells, are involved in liver inflammation. Proteins such as fibroblast growth factors, acetyl-coenzyme A carboxylases, and nuclear factor erythroid 2-related factor 2 are involved in liver metabolism and inflammation, which are potential targets for NASH treatment. This review focuses on the effects of metabolic disease-induced extrahepatic inflammation, liver inflammation, and the cellular and molecular mechanisms of liver metabolism on the development and progression of NAFLD and NASH, as well as the associated treatments.

Ionizing radiation promotes, whereas calorie restriction suppresses, NASH and hepatocellular carcinoma in mice

The pathological conditions of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis (NASH) are the major risk factors for hepatocellular carcinoma (HCC). Exposure to DNA-damaging agents such as ionizing radiation is another risk factor for HCC; calorie restriction (CR), however, effectively delays the onset of radiation-induced HCC. We investigated whether NASH is relevant to radiation-induced HCC and the cancer-preventing effect of CR. Eight-day-old male B6C3F1 mice were irradiated with 3.8 Gy of X-rays and then fed a standard diet or 30% CR diet from 49 days of age until necropsy, which was performed from 56 to 600 days with ~100-day intervals to assess both pathological changes and gene expression levels. We found that early-life exposure to radiation accelerated lipid accumulation and NASH-like histopathological changes in the liver, accompanied by accelerated development of HCC. CR ameliorated the changes in lipid metabolism in the liver and reversed the NASH-like pathology, which effectively delayed HCC development. Gene-expression profiling revealed the radiation-related activation and CR-related suppression of the peroxisome proliferator-activated receptor gamma/Cd36 pathway of transmembrane fatty-acid translocation before development of the NASH-like state. Thus, early-life exposure to radiation affects lipid metabolism and induces a steatoinflammatory microenvironment that favors HCC development. Therefore, targeting this pathway by CR (or measures that mimic CR) may be a promising strategy for preventing HCC caused by either radiation or other DNA-damaging agents.

Natural polysaccharides protect against diet-induced obesity by improving lipid metabolism and regulating the immune system

Unhealthy dietary patterns-induced obesity and obesity-related complications pose a great threat to human health all over the world. Accumulating evidence suggests that the pathophysiology of obesity and obesity-associated metabolic disorders is closely associated with dysregulation of lipid and energy metabolism, and metabolic inflammation. In this review, three potential anti-obesity mechanisms of natural polysaccharides are introduced. Firstly, natural polysaccharides protect against diet-induced obesity directly by improving lipid and cholesterol metabolism. Since the immunity also affects lipid and energy metabolism, natural polysaccharides improve lipid and energy metabolism by regulating host immunity. Moreover, diet-induced mitochondrial dysfunction, prolonged endoplasmic reticulum stress, defective autophagy and microbial dysbiosis can disrupt lipid and/or energy metabolism in a direct and/or inflammation-induced manner. Therefore, natural polysaccharides also improve lipid and energy metabolism and suppress inflammation by alleviating mitochondrial dysfunction and endoplasmic reticulum stress, promoting autophagy and regulating gut microbiota composition. Specifically, this review comprehensively summarizes underlying anti-obesity mechanisms of natural polysaccharides and provides a theoretical basis for the development of functional foods. For the first time, this review elucidates anti-obesity mechanisms of natural polysaccharides from the perspectives of their hypolipidemic, energy-regulating and immune-regulating mechanisms.